In order to provide a suitably preload on the running bearings such as antifriction bearings in a spindle device, for example the grinding wheel spindle head for an internal grinder, bearings at one end of the spindle are slidable in a longitudinal direction in the housing and the preload is applied to them by means of spring force or the like. When the rotary spindle elongates somewhat by reason of thermal expansion due to the heat generated by the spindle rotation, the slidable bearing moves longitudinally to compensate for the elongation and thereby maintains a suitable preload.
However, this structure has the defect that the slidable bearing does not slide freely so as to compensate for thermal expansion because of excessive friction force on the sliding surfaces of the bearing and housing in case a high radial load is applied to the rotary spindle, for example by means of a belt by which the spindle is driven.